Four important factors in the production of Italian espresso: 4m theory

Macinazione: the right ground coffee beans are too thick or too fine to make a thick and delicious espresso. Coffee powder is too thick, the gap of coffee powder in the filter is too big, the resistance to water is not enough, the flow rate of coffee is too fast, it is easy to cause insufficient extraction, coffee is tasteless. It is also wrong for coffee powder to be ground too fine, because the resistance is too high, and the hot water stays in the filter for too long.